Worm Breeder's Gazette 8(2): 15
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
Using the laser to perform microsurgery on embryos as described in the previous newsletter we have asked whether fusion of a cell from one lineage with cytoplasm from a second lineage can lead to expression of a differentiation marker specific to the second lineage. Our preliminary experiments indicate that this can occur for at least one and possibly three different markers. In the first set of experiments, a non-gut precursor cell (an AB descendant) was fused to cytoplasm from a gut precursor cell (P1). The posterior egg shell of a 2-cell embryo was punctured and the P1 nucleus extruded with a small amount of cytoplasm. The extruded P1 fragment was separated from the embryo, and the P1 cytoplast ( enucleated cell) remaining inside the shell was fused to a descendant of AB. After development overnight (to a terminal phenotype of several hundred cells without morphogenesis), more than 50% of the embryos showed the localized autofluorescence characteristic of differentiated gut cells in a normal embryo. In control experiments with no fusion following P1 enucleation, no autofluorescence was usually observed. Some embryos in both types of experiments showed diffuse low-level fluorescence perhaps resulting from degeneration. In a second experiment, difficult to perform and successfully accomplished only once, the P1 nucleus was removed from one side of a 1-cell embryo (to avoid possible loss of posterior determinants) just prior to completion of first cleavage, leading to reformaton of a 1- cell embryo with an AB nucleus. This embryo also developed to several hundred cells including differentiated cells of typical body-muscle appearance, and showed twitching indicative of muscle contraction. Twitching was never observed in control embryos such as those described above. (This experimental embryo did not show gut autofluorescence. Embryos in the first set of experiments were not observed to twitch, but only their terminal phenotypes were examined, so that twitching during development would have been missed.) In a third set of experiments the AB nucleus was removed from the anterior pole during the first cleavage, leading to formation of a 1- cell embryo with a P1 nucleus. These embryos also developed to several hundred cells, often including a group of small cells at the anterior end whose nuclei appeared typical of neuronal nuclei in the Nomarski microscope. A better marker is needed to show that these are neuronal cells. Control experiments in which AB was enucleated after first cleavage showed no such cells. We conclude that cytoplasmic factors can alter the potential of early nuclei for lineage-specific patterns of expression.